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Experimental investigation on the characteristics of inline dimple-based SAH with dimple pitch variation

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Abstract

In this work, the performance of an inline dimpled-based absorber plate solar air heater (IDPSAH) is studied in relation to pitch, a system parameter, and air flow rate (Mair), an operating parameter. In this regard, two alternative IDPSAH with pitch ratios 0.88 and 1.33 have been experimentally evaluated on alternative days by altering the Mair from 0.010 to 0.053 kg s-1 (Proportional Re range: 1971.66–11,113.24) and the result are compared with flat plate solar air heater (FPSAH). For performance evaluation and comparative research, various parameters have been studied, including air temperature difference, efficiencies (ηinst, ηeff, ηdaily), global heat loss coefficient, heat removal factor, collector efficiency, top loss, area averaged Nusselt number (Nuavg), and friction factor (favg), among others. The effective efficiency reaches its maximum at a particular Mair and then begins to decline, but the instantaneous and daily efficiency of IDPSAH and FPSAH increases continuously. Due to a decrease top loss, the efficiency of IDPSAH is higher than FPSAH. The instantaneous efficiency of IDPSAH at pitch ratio 0.88 is 1.13–1.53 times greater than the instantaneous efficiency of IDPSAH at pitch ratio 1.33 and it is 1.21–1.86 times higher than FPSAH. With an increase in Re, the favg value decreases; while, the Nuavg of both the FPSAH and IDPSAH increases. In comparison with IDPSAH with pitch ratio 1.33, the Nuavg of IDPSAH at pitch ratio 0.88 is 1.23–1.41 times higher, and it is 1.68–2.12 times higher than FPSAH. In comparison with IDPSAH at pitch ratio 1.33 and FPSAH, the favg of IDPSAH at pitch ratio 0.88 is higher. However, there is a significant enhancement in overall performance of IDPSAH than the FPSAH.

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Abbreviations

FPSAH:

Flat absorber plate Solar air heater or Flat absorber plate Solar air collector

IDPSAH:

Inline Dimpled absorber Plate Solar air heater or Inline Dimple absorber Plate Solar air collector

D p :

Print or imprint diameter of dimple, m

d h :

Indention depth of dimple, m

S T , S L :

Span wise and Stream wise dimple pitch, m

D h :

Equivalent diameter of SAH duct, m

W, H :

Width and height of SAH duct, m

W/H :

Aspect ratio of SAH duct

A pl :

Surface area of plate (glass or absorber), m2

N gl :

Number of glazing (tempered glass)

t gl :

Thickness of glazing (tempered glass), m

tins :

Insulation thickness, m

\({\overline{T}}_{{\text{airin}}} ,{\overline{T}}_{{\text{airout}}}\) :

Mean temperature of inlet air and outlet air in a SAH, K

\({M}_{{\text{air}}}\) :

Air flow rate in SAH, kg s-1

\({\overline{V}}_{{\text{i}}},{\overline{V}}_{0}\) :

Mean air flow velocity at inlet and outlet of the SAH, m s-1

\({A}_{{\text{i}}}{,A}_{0}\) :

Inlet and outlet area of solar duct, m2

\({Q}_{{\text{ext}}}\) :

Amount of useful heat extracted rate for air type solar collector, W

\({Q}_{{\text{rec}}}\) :

Amount of heat received rate by the collector surface (absorber plate) in air type solar collector, W

\({\eta }_{{\text{inst}}}\) :

SAH instantaneous (or thermal) efficiency

I :

Solar irradiation or net global irradiation fall on solar collector plane, W m-2

α:

Absorber plate’s absorptivity

τ:

Glass’s transmissivity

\({C}_{{\text{pair}}}\) :

Air specific heat, J kg-1 K-1

\({Q}_{{\text{eff}}}\) :

Effective heat transfer rate, W

\({P}_{{\text{bl}}}\) :

Pumping energy required by the blower, W

\({\eta }_{{\text{eff}}}\) :

SAH effective Efficiency

Nuavg :

Area averaged Nusselt number

h avg :

The area averaged convective heat transfer coefficient, W m−2 K-1

ka :

The fluid (air) thermal conductivity W m-1 K-1

Re:

Reynolds number

μa :

The air viscosity, N s m-2

ρ a :

The air density, kg m-3

f avg :

Area averaged friction factor

\(\Delta {P}_{{\text{d}}}\) :

Pressure drop, Pa

L :

Absorber plate’s length, m

\({F}_{0}, {F}_{{\text{R}}}\) :

SAH heat removal factor based on air outlet and inlet temperature

F/ :

The collector efficiency or SAH efficiency factor of SAH

\({\eta }_{{\text{daily}}}\) :

SAH daily Efficienc

\({Q}_{{\text{top}}}\) :

Amount of heat loss rate from the top of the tempered glass, W

\({T}_{{\text{gl}}}\) :

Tempered glass temperature, K

\({T}_{{\text{amb}}}\) :

Ambient (surrounding air) temperature, K

\({h}_{{\text{w}}}\) :

Wind heat transfer coefficient (because of convection), W m−2 K-1

\({h}_{{\text{r}}}\) :

Radiative heat transfer Coefficient, W m−2 K-1

\({V}_{{\text{w}}}\) :

Wind velocity, m s-1

σ:

Stefan–Boltzmann Constant, W m−2 K-4

\({\epsilon }_{{\text{g}}}\) :

Glass covers emissivity

\({T}_{{\text{s}}}\) :

Temperature of the sky, K

\({U}_{{\text{L}}}\) :

SAH global heat loss (total heat loss) coefficient, W m−2 K-1

p/e :

Ratio of roughness pitch to roughness height

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  1. Department of Mechanical Engineering, IIT (ISM) Dhanbad, Dhanbad, Jharkhand, 826004, India

    Sudharani Panda & Rakesh Kumar

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  1. Sudharani Panda
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Conceptualization contributed by SP, RK; data curation contributed by SP; formal analysis contributed by SP; investigation contributed by SP; methodology contributed by SP, RK; roles/writing—original draft contributed by SP; writing—review & editing contributed by SP, RK; supervision contributed by RK.

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Correspondence to Rakesh Kumar.

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Panda, S., Kumar, R. Experimental investigation on the characteristics of inline dimple-based SAH with dimple pitch variation. J Therm Anal Calorim (2024). https://doi.org/10.1007/s10973-024-13088-6

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